Tag: neuroscience

Why is the number of friendships that we can actively maintain limited to 150? The evolutionary psychologist and anthropologist Robin Dunbar at the University of Oxford is a pioneer in the study of friendship. Over several decades, he and his colleagues have investigated the nature of friendship and social relationships in non-human primates and humans. His research papers and monographs on social networks, grooming, gossip and friendship have accumulated tens of thousands of academic citations but he may be best known in popular culture for “Dunbar’s number“, the limit to the number of people with whom an individual can maintain stable social relationships. For humans, this number is approximately 150 although there are of course variations between individuals and also across one’s lifetime. The expression “stable social relationships” is what we would call friends and family members with whom we regularly interact. Most of us may know far more people but they likely fall into a category of “acquaintances” instead of “friends”. Acquaintances, for example, are fellow students and colleagues who we occasionally meet at work, but we do not regularly invite them over to share meals or swap anecdotes as we would do with our friends.

Dunbar recently reviewed more than two decades of research on humans and non-human primates in the article “The Anatomy of Friendship” and outlines two fundamental constraints: Time and our brain. In order to maintain friendships, we have to invest time. As most of us intuitively know, friendship is subject to hierarchies. Dunbar and other researchers have been able to study these hierarchies scientifically and found remarkable consistency in the structure of the friendship hierarchy across networks and cultures. This hierarchy can be best visualized as concentric circles of friendship. The innermost core circle consists of 1-2 friends, often the romantic partner and/or the closest family member. The next circle contains approximately 5 very close friends, then progressively wider circles until we reach the maximum of about 150. The wider the circle becomes, the less time we invest in “grooming” or communicating with our friends. The social time we invest also mirrors the emotional closeness we feel. It appears that up to 40% of our social time is invested in the inner circle of our 5 closest friends, 20% to our circle of 15 friends, and progressively less. Our overall social time available to “invest’ in friendships on any given day is limited by our need to sleep and work which then limits the number of friends in each circle as well as the total number of friendships.

The Circles of Friendship – modified from R Dunbar, The Anatomy of Friendship (2018)

The second constraint which limits the number of friendships we can maintain is our cognitive capacity. According to Dunbar, there are at least two fundamental cognitive processes at play in forming friendships. First, there needs to be some basis of trust in a friendship because it represents implicit social contracts, such as a promise of future support if needed and an underlying promise of reciprocity – “If you are here for me now, I will be there for you when you need me.” For a stable friendship between two individuals, both need to be aware of how certain actions could undermine this implicit contract. For example, friends who continuously borrow my books and seem to think that they are allowed to keep them indefinitely will find that there are gradually nudged to the outer circles of friendship and eventually cross into the acquaintance territory. This is not only because I feel I am being taken advantage off and the implicit social contract is being violated but also because they do not appear to put in the mental effort to realize how much I value my books and how their unilateral “borrowing” may affect me. This brings us to “mentalizing”, the second important cognitive component that is critical for stable friendships according to Dunbar. Mentalizing refers to the ability to read or understand someone else’s state of mind. To engage in an active dialogue with friends not only requires being able to read their state of mind but also infer the state of mind of people that they are talking about. These levels of mentalizing (‘I think that you feel that she was correct in …..) appear to hit a limit around four or five. Dunbar cites the example of how at a gathering, up to four people can have an active conversation in which each person is closely following what everyone else is saying but once a fifth person joins (the fifth wheel!), the conversation is likely to split up into two conversations and that the same is true for many TV shows or plays in which scenes will rarely depict more than four characters actively participating in a conversation.

Has the digital age changed the number of friends we can have? The prior research by Dunbar and his colleagues relied on traditional means of communication between friends such as face-to-face interactions and phone calls but do these findings still apply today when social media such as Facebook and Twitter allow us to have several hundred or even thousands of “friends” and “followers”? The surprising finding is that online social networks are quite similar to traditional networks! In a study of Facebook and Twitter social media networks, Dunbar and his colleagues found that social media networks exhibit a hierarchy of friendship and numbers of friends that were extremely similar to “offline” networks. Even though it is possible to have more than a thousand “friends” on Facebook, it turns out that most of the bidirectional interactions with individuals are again concentrated in very narrow circles of approximately 5, 15 and 50 individuals. Social media make it much easier to broadcast information to a broad group of individuals but this sharing of information is very different from the “grooming” of friendships which appears to be based on reciprocity in terms of building trust and mentalizing.

There is a tendency to believe that the Internet has revolutionized all forms of human communication, a belief which falls under the rubric of “internet-centrism” (See the article “Is Internet-Centrism a Religion“) according to the social researcher Evgeny Morozov. Dunbar’s research is an important reminder that core biological and psychological principles such as the anatomy of friendship in humans have evolved over hundreds of thousands of years and will not be fundamentally upstaged by technological improvements in communication. Friendship and its traditional limits are here to stay.

Can neuroscience help identify individuals who are most prone to engage in violent criminal behavior? Will it help the legal system make decisions about sentencing, probation, parole or even court-mandated treatments? A panel of researchers lead by Dr. Russell Poldrack from Stanford University recently reviewed the current state of research and outlined the challenges that need to be addressed for “neuroprediction” to gain traction. The use of scientific knowledge to predict violent behavior is not new. Social factors such as poverty and unemployment increase the risk for engaging in violent behavior. Twin and family studies suggest that genetic factors also significantly contribute to antisocial and violent behavior but the precise genetic mechanisms remain unclear. A substantial amount of research has focused on genetic variants of the MAOA gene (monoamine oxidase A, an enzyme involved in the metabolism of neurotransmitters). Variants of MAOA have been linked to increased violent behavior but these variants are quite common – up to 40% of the US population may express this variant! As pointed out by John Horgan in Scientific American, it is impossible to derive meaningful predictions of individual behavior based on the presence of such common gene variants.

One fundamental problem of using social and genetic predictors of criminal violent behavior in the legal setting is the group-to-individual problem. Carrying a gene or having been exposed to poverty as a child may increase the group risk for future criminal behavior but it tells us little about an individual who is part of the group. Most people who grow up in poverty or carry the above-mentioned MAOA gene variant do not engage in criminal violent behavior. Since the legal system is concerned with an individual’s guilt and his/her likelihood to commit future violent crimes, group characteristics are of little help. This is where brain imaging may represent an advancement because it can assess individual brains. Imaging individual brains might provide much better insights into a person’s brain function and potential for violent crimes than more generic assessments of behavior or genetic risk factors.

Poldrack and colleagues cite a landmark study published in 2013 by Eyal Aharoni and colleagues in which 96 adult offenders underwent brain imaging with a mobile MRI scanner before being released from one of two New Mexico state correctional facilities. The prisoners were followed for up to four years after their release and the rate of being arrested again was monitored.

This study found that lower activity in the anterior cingulate cortex (ACC- an area of the brain involved in impulse control) was associated with a higher rate being arrested again (60% in participants with lower ACC activity, 46% in those with higher ACC activity). The sample size and rate of re-arrest was too small to see what the predictive accuracy was for violent crime re-arrests (as opposed to all re-arrests). Poldrack and colleagues lauded the study for dealing with the logistics of performing such complex brain imaging studies by using a mobile MRI scanner at the correctional facilities as well as prospectively monitoring their re-arrest rate. However, they also pointed out some limitations of the study in terms of the analysis and the need to validate the results in other groups of subjects.

Brain imaging is also fraught with the group-to-individual problem. Crude measures such as ACC activity may provide statistically significant correlations for differences between groups but do not tell us much about how any one individual is likely to behave in the future. The differences in the re-arrest rates between the high and low ACC activity groups are not that profound and it is unlikely that they would be of much use in the legal system. So is there a future for “neuroprediction” when it comes to deciding about the sentencing or parole of individuals?

Poldrack and colleagues outline some of the challenges of brain imaging for neuroprediction. One major challenge is the issue of selecting subjects. Many people may refuse to undergo brain imaging and it is quite likely that those who struggle with impulse control and discipline may be more likely to refuse brain scanning or move during the brain scanning process and thus distort the images. This could skew the results because those most likely to succumb to impulse control may never be part of the brain imaging studies. Other major challenges include using large enough and representative sample sizes, replicating studies, eliminating biases in the analyses and developing a consensus on the best analytical methods. Addressing these challenges would advance the field.

It does not appear that neuroprediction will become relevant for court cases in the near future. The points outlined by the experts remind us that we need to be cautious when interpreting brain imaging data and that solid science is required for rushing to premature speculations and hype about using brain scanners in court-rooms.

How many hours of sleep does the average person require? The American Academy of Sleep Medicine and the Sleep Research Society recently convened an expert panel which reviewed over 5,000 scientific articles and determined that sleeping less than 7 hours in adults (ages 18-60) was associated with worsening health, such as increased obesity and diabetes, higher blood pressure as well as an increased risk of stroke and heart disease. In addition to increasing the risk for illnesses, inadequate sleep is also linked to impaired general functioning, as evidenced by suppressed immune function, deficits in attention and memory, and a higher rate of errors and accidents. Since at least one third of adults report that they sleep less than 7 hours a day (as assessed by the Centers for Disease Control and Prevention in a survey of 444,306 adults), one can legitimately refer to insufficient sleep as a major public health issue. Even though insufficient sleep and other sleep disorders have reached epidemic-like proportions affecting hundreds of millions of adults world-wide, they are not adequately diagnosed and treated when compared to medical risk factors and conditions. For example, in most industrialized countries, primary care physicians perform annual blood pressure and cholesterol level checks, but do not routinely monitor the sleep duration and quality of their patients.
One reason for this may be the complexity of assessing sleep. Checking the blood cholesterol level is quite straightforward and provides a reasonably objective value which is either below or above the recommended cholesterol thresholds. However, when it comes to sleep, matters become more complicated. The above-mentioned expert panel acknowledged that there can be significant differences in the sleep requirements of individuals. Those who suffer from illnesses or have incurred “sleep debt” may require up to 9 hours of sleep, and then there are also significant environmental and genetic factors which can help determine the sleep needs of an individual. The average healthy person may need at least seven hours of sleep but there probably groups of individuals who can function well with merely 6 hours while others may need 9 hours of sleep. Then there is also the issue of the sleep quality. Sleeping for seven hours between 10 pm and 5 am has a higher quality of sleep than sleeping between 6 am and 1 pm because the latter will be associated with many more spontaneous awakenings and interruptions as well as less slow-wave sleep (a form of “deep sleep” characterized by classical slow wave patterns on a brain EEG recording during sleep). Unlike the objective cholesterol blood test, a true assessment of sleep would require an extensive sleep questionnaire asking details about sleep history and perhaps even recording sleep with activity monitors or EEGs.

Another reason for why insufficient sleep is not treated like other risk factors such as cholesterol and blood pressure is that there aren’t any easy fixes for poor sleep and the science of how poor sleep leads to cognitive deficits, diabetes and heart disease is still very much a topic of investigation.

In the case of cholesterol, numerous studies have shown that cholesterol levels can be effectively lowered by taking a daily medication such as a statin and that this intervention clearly lowers the risk of heart attacks and stroke. Furthermore, the science of how cholesterol causes stroke and heart disease has been worked out quite well by identifying the molecular mechanisms of how cholesterol contributes to the build-up of plaque in the arteries which can then lead to heart attacks and stroke. When it comes to sleep, on the other hand, multi-faceted interventions are required to restore healthy sleep levels. Medications to help patients sleep can be used in certain circumstances for a limited time but they are not a long-term solution. Instead, improving sleep requires individualized solutions such as developing a sleep schedule of fixed bed-times, minimizing the use of digital screens in the bedroom, and avoiding caffeine, large meals, nicotine or alcohol just before bedtime. The complexity of assessing and treating insufficient sleep also makes it very difficult to prove the efficacy of interventions. Controlled clinical studies can demonstrate that a cholesterol-lowering medication reduces the risk of heart attacks by treating thousands of patients with the active medication when compared to thousands of patients who receive a placebo, but how do you test the efficacy of individualized sleep interventions in thousands of patients?

Understanding the precise mechanisms by which insufficient sleep impairs our functioning and health has therefore become a major topic of research with significant advances that have been made in the past decades. Correlative studies which link poor sleep to worse health cannot prove that it is the inadequate sleep which caused the problems, but studies in which human subjects undergo well-defined sleep deprivation for a defined number of hours coupled with EEGs, brain imaging studies and cognitive assessments are providing important insights into how poor sleep can affect brain function. The sleep researcher Matthew Walker at the University of California and his colleagues recently reviewed some of the key studies in sleep research and identified some of the major categories of brain function impairment as a consequence of sleep deprivation:

1. Attention:

Several studies of human subjects have consistently shown that sleep deprivation leads to a significant decrease in the ability to pay attention to tasks. Some studies have kept subjects awake for 24 hours at a stretch whereas other studies merely restricted sleep to a few hours a night and monitored the performance. Importantly, one study that restricted sleep to less than 3 hours for one week was able to show that the attentiveness and performance of subjects recovered rapidly once the sleep-deprived subjects were allowed to sleep for 8 hours but it still did not return back to the levels of those without sleep deprivation. This means that the after-effects of sleep deprivation can linger for days even when we start sleeping normally.

2. Memory:

The impairment of working memory (the temporary memory we use to make decisions and complete tasks) is another key feature of sleep deprivation. Brain imaging studies have been able to identify specific abnormalities in certain areas of the brain that are critical for the “working memory” function such as the dorsolateral prefrontal cortex and thus provide somewhat objective measures of cognitive impairment. Interestingly, placing magnetic coils around the head of sleep-deprived subjects to initiate TMS (transcranial magnetic stimulation) has been reported to help restore some of the loss of visual memory, however, Walker and colleagues note that the benefits of TMS in sleep deprivation are not always consistent and reproducible.

3. Responding to negative stimuli

Sleep deprivation increases responses to negative stimuli such as fear. For example, when subjects who had one night of sleep deprivation were shown images of weapons, snakes or mutilations, their aversion responses were much stronger than those of control subjects. Hyper-responsiveness of the amygdala, the part of the brain which processes emotional reactions, is thought to be one major element in these exaggerated responses of sleep-deprived subjects.

Walker and colleagues note that not all changes seen in the brain imaging studies are necessarily detrimental. In fact, some of these changes may be adaptations that have evolved to help our brains cope with the stress of sleep deprivation. Even though significant progress has been made in sleep deprivation research, understanding differences between individuals in terms of how and why they respond differently to sleep deprivation, distinguishing the mechanisms of beneficial adaptations in brain function from detrimental responses and also developing new studies that study the effects of chronic sleep deprivation – one that occurs over a period of weeks and months and thus mimics real-life sleep deprivation – instead of the short-term acute sleep deprivation studies that are currently performed in the laboratory are major challenges for sleep researchers. Hopefully, advances in sleep research will lead to a better understanding of sleep health and ultimately also translate into sleep becoming an integral part of medical exams in order to address this burgeoning public health problem.

“It’s empathy that makes us help other people. It’s empathy that makes us moral.” The economist Paul Zak casually makes this comment in his widely watched TED talk about the hormone oxytocin, which he dubs the “moral molecule”. Zak quotes a number of behavioral studies to support his claim that oxytocin increases empathy and trust, which in turn increases moral behavior. If all humans regularly inhaled a few puffs of oxytocin through a nasal spray, we could become more compassionate and caring. It sounds too good to be true. And recent research now suggests that this overly simplistic view of oxytocin, empathy and morality is indeed too good to be true.

Many scientific studies support the idea that oxytocin is a major biological mechanism underlying the emotions of empathy and the formation of bonds between humans. However, inferring that these oxytocin effects in turn make us more moral is a much more controversial statement. In 2011, the researcher Carsten De Dreu and his colleagues at the University of Amsterdam in the Netherlands published the study Oxytocin promotes human ethnocentrism which studied indigenous Dutch male study subjects who in a blinded fashion self-administered either nasal oxytocin or a placebo spray. The subjects then answered questions and performed word association tasks after seeing photographic images of Dutch males (the “in-group”) or images of Arabs and Germans, the “out-group” because prior surveys had shown that the Dutch public has negative views of both Arabs/Muslims and Germans. To ensure that the subjects understood the distinct ethnic backgrounds of the target people shown in the images, they were referred to typical Dutch male names, German names (such as Markus and Helmut) or Arab names (such as Ahmed and Youssef).

Oxytocin increased favorable views and word associations but only towards in-group images of fellow Dutch males. The oxytocin treatment even had the unexpected effect of worsening the views regarding Arabs and Germans but this latter effect was not quite statistically significant. Far from being a “moral molecule”, oxytocin may actually increase ethnic bias in society because it selectively enhances certain emotional bonds. In a subsequent study, De Dreu then addressed another aspect of the purported link between oxytocin and morality by testing the honesty of subjects. The study Oxytocin promotes group-serving dishonesty showed that oxytocin increased cheating in study subjects if they were under the impression that dishonesty would benefit their group. De Dreu concluded that oxytocin does make us less selfish and care more about the interest of the group we belong to.

These recent oxytocin studies not only question the “moral molecule” status of oxytocin but raise the even broader question of whether more empathy necessarily leads to increased moral behavior, independent of whether or not it is related to oxytocin. The researchers Jean Decety and Jason Cowell at the University of Chicago recently analyzed the scientific literature on the link between empathy and morality in their commentary Friends or Foes: Is Empathy Necessary for Moral Behavior?, and find that the relationship is far more complicated than one would surmise. Judges, police officers and doctors who exhibit great empathy by sharing in the emotional upheaval experienced by the oppressed, persecuted and severely ill always end up making the right moral choices – in Hollywood movies. But empathy in the real world is a multi-faceted phenomenon and we use this term loosely, as Decety and Cowell point out, without clarifying which aspect of empathy we are referring to.

Decety and Cowell distinguish at least three distinct aspects of empathy:

1. Emotional sharing, which refers to how one’s emotions respond to the emotions of those around us. Empathy enables us to “feel” the pain of others and this phenomenon of emotional sharing is also commonly observed in non-human animals such as birds or mice.

2. Empathic concern, which describes how we care for the welfare of others. Whereas emotional sharing refers to how we experience the emotions of others, empathic concern motivates us to take actions that will improve their welfare. As with emotional sharing, empathic concern is not only present in humans but also conserved among many non-human species and likely constitutes a major evolutionary advantage.

3. Perspective taking, which – according to Decety and Cowell – is the ability to put oneself into the mind of another and thus imagine what they might be thinking or feeling. This is a more cognitive dimension of empathy and essential for our ability to interact with fellow human beings. Even if we cannot experience the pain of others, we may still be able to understand or envision how they might be feeling. One of the key features of psychopaths is their inability to experience the emotions of others. However, this does not necessarily mean that psychopaths are unable to cognitively imagine what others are thinking. Instead of labeling psychopaths as having no empathy, it is probably more appropriate to specifically characterize them as having a reduced capacity to share in the emotions while maintaining an intact capacity for perspective-taking.

In addition to the complexity of what we call “empathy”, we need to also understand that empathy is usually directed towards specific individuals and groups. De Dreu’s studies demonstrated that oxytocin can make us more pro-social as long as it benefits those who we feel belong to our group but not necessarily those outside of our group. The study Do you feel my pain? Racial group membership modulates empathic neural responses by Xu and colleagues at Peking University used fMRI brain imaging in Chinese and Caucasian study subjects and measured their neural responses to watching painful images. The study subjects were shown images of either a Chinese or a Caucasian face. In the control condition, the depicted image showed a face being poked with a cotton swab. In the pain condition, study subjects were shown a face of a person being poked with a needle attached to syringe. When the researchers measured the neural responses with the fMRI, they found significant activation in the anterior cingulate cortex (ACC) which is part of the neural pain circuit, both for pain we experience ourselves but also for empathic pain we experience when we see others in pain. The key finding in Xu’s study was that ACC activation in response to seeing the painful image was much more profound when the study subject and the person shown in the painful image belonged to the same race.

As we realize that the neural circuits and hormones which form the biological basis of our empathy responses are so easily swayed by group membership then it becomes apparent why increased empathy does not necessarily result in behavior consistent with moral principles. In his essay “Against Empathy“, the psychologist Paul Bloom also opposes the view that empathy should form the basis of morality and that we should unquestioningly elevate empathy to virtue for all:

“But we know that a high level of empathy does not make one a good person and that a low level does not make one a bad person. Being a good person likely is more related to distanced feelings of compassion and kindness, along with intelligence, self-control, and a sense of justice. Being a bad person has more to do with a lack of regard for others and an inability to control one’s appetites.”

I do not think that we can dismiss empathy as a factor in our moral decision-making. Bloom makes a good case for distanced compassion and kindness that does not arise from the more visceral emotion of empathy. But when we see fellow humans and animals in pain, then our initial biological responses are guided by empathy and anger, not the more abstract concept of distanced compassion. What we need is a better scientific and philosophical understanding of what empathy is. Empathic perspective-taking may be a far more robust and reliable guide for moral decision-making than empathic emotions. Current scientific studies on empathy often measure it as an aggregate measure without teasing out the various components of empathy. They also tend to underestimate that the relative contributions of the empathy components (emotion, concern, perspective-taking) can vary widely among cultures and age groups. We need to replace overly simplistic notions such as oxytocin = moral molecule or empathy = good with a more refined view of the complex morality-empathy relationship guided by rigorous science and philosophy.

I recently wrote a short essay for 3Quarksdaily on the three second rule of temporal perception and processing in the human brain. It is comparatively easy to measure the thresholds that our brain uses to create temporal structure, i.e. the minimum time interval required to correctly tell apart the sequence of brief sounds or images. It lies somewhere in the range of 30 milliseconds to 60 milliseconds. If healthy subjects hear two auditory clicks (one in the right ear and one in the left ear) which are only 10 milliseconds apart, they may be able to identify them as two distinct stimuli, but they may not be able to say which one came first.

Temporal integration, on the other hand, refers to combining sensory information and creating the sense of a subjective present or the perception of a “now”. It is not possible to directly measure it, but many observational studies point to a “three second rule” of temporal integration in the brain. One of these studies involved the analysis of poetic meter and was conducted by the chairman of the department in which I used to work when I was a student. The study found that the average time it takes to recite individual verses of poems from all around the world is approximately three seconds. Since each verse (the authors use the more generic term “LINE” to accomodate poems which use a different orthrographic notation or which allow for pauses when reciting long verses) is considered to be an independent unit that is intended to evoke certain poetic “moments”, the authors surmise that the global convergence of verse length may be due to the fact that our brain is most comfortable with three-second intervals to create the sensation of the “now”. This is obviously anecdotal and observational, and not a definitive finding, but it is still fascinating. It does not “prove” that our brain perceives the “now” in three second intervals, but when combined with other cognitive studies of temporal integration, it supports the notion that three seconds may be an important temporal unit for our brain.

You should consider reading some of the original references that are linked in my 3Quraksdaily essay, such as the classic study published in the Poetry magazine, which is (thankfully) open access and can be read by everyone. It is a remarkable example of how a collaboration between a cognitive scientist (my former chairman) and a poet which won a prestigious poetry award when it was published in 1983.